The sent invention relates to a process for cleansing contaminants, such as oil, PCB, PAH, heavy metals, lipids and the like from a heterogeneous material, such as sand, gravel, earth, oil gravel, asphalt, drill borings ("kaks"), sewage sludge and the like.
Contamination of dissimilar materials for example in connection with industrial equipment, dump locations or beaches which are contaminated by for example an oil spill, is a well known and increasing problem, and large resources are employed to find solutions to purifying such masses. The solutions must be able to be carried out practically and economically. Several reports describe big environmental problems connected with such contaminated materials. In this connection various hydrocarbon compounds are often mentioned such as oil-like compounds, hydrocarbons which either have coupled on chlorine or bromine groups (PCB), or dissimilar types of aromatic compounds (PAH). The said compounds are all soluble in nonpolar solvents. That is to say they are dissolved slightly in water, and in an association that will be energetically favourable to exclude water. By virtue of the water-repelling property these media will readily adhere to solid surfaces, such as stone, gravel and earth. Furthermore water which runs through these materials will not wash away or dilute these hydrophobic solvents.
A number of locations are mapped where such contaminated materials constitute a significant environmental problem.
In addition to the materials consisting of hydrophobic contaminants they will also consist of various heavy metals, which because of their toxicity also represent an environmental problem.
Today it is usual to "clean" such dump materials by combusting the contamination of the stone materials. However this is very expensive since the costs of such burning off is related to the weight of the materials and to the combustion value, that is to say how much energy which can be utilised by such a combustion. Materials from industrial sites or dumps consist mainly of stone/gravel, that is to say the weight is high and the combustion value low.
There is therefore a need for alternative solutions. Such a solution is described in PCT/NO96/00185 which relates to a sorption agent comprising the plant family Sphagnum for the sorption of hydrophobic compounds where the sphagnum plant is substantially wholly or partially dried. The publication also describes the application of the plant material for removing hydrophobic compounds from solutions and emulsions, together with it being employed directly on materials which are contaminated with hydrophobic compounds by being rubbed against the material. For example it is mentioned that the plant material can be rubbed directly against an oil spill for example in a workshop hall.
However there are other problems which must be solved in order to cleanse contaminants from a heterogeneous material, such as stone and earth. In such materials the oil is an integrated part of the material, that is to say it envelops and sticks together with the dissimilar components of the material so that it becomes a relatively viscous, tacky material. Furthermore the material is formed of particles of relatively small size so that one cannot apply the moss for example to "dry" the particles as one for example can dry off a workshop floor.
The present invention aims therefore to produce a solution for cleansing such materials. When an effective absorptive or adsorptive material is added to a material, and the material and the sorption material are kneaded and tumbled together a certain time, the contaminants will, whether they are hydrophobic compounds or for example heavy metals, be transferred from the material to the sorption agent, assuming that the sorption agent has stronger ad- and/or absorptive properties than the material, and that the compounds are detached from the material by the friction which is created during the kneading/tumbling process, or by means of water/solvents. Even for an effective sorption agent this will not be added if the contaminants are solidified and very strongly fixed to particles of the material. Also this problem is aimed to be solved with the present invention.
A further problem in the cleaning of such materials is that the material, such as sand, gravel and earth, with respect to the size of the particles constitutes a heterogeneous mixture, and often comprising a significant proportion of smaller particles, right down to a size of only some few microns in diameter. A problem which cannot be solved with the afore-mentioned invention is therefore separating the sorption agent from these in part very small particles. The present invention therefore aims to solve this problem also.
The present invention describes therefore a process for cleaning various types of materials, such as for example fill materials, gravel, earth and the like by removing the dissimilar contaminants, such as hydrophobic contaminants as for example oil, PCB and PAH, and heavy metals from the materials.